1. Homeostasis and Excretion
Christen Fechtel
Deanna Dang
Stephanie Daniel

2. Intro to Homeostasis
Maintenance of physiological systems by maintaining a stable internal environment
water and solute concentrations
Metabolism and disposal of metabolic waste
Two key processes: osmoregulation and excretion

3. IB Syllabus!

4. Osmoregulation
How animals regulate solute concentrations and balance the gain and loss of water in blood, tissues, and cytoplasm-
the homeostasis of osmolarity in body fluids
Regulates chemical composition of body fluids
Controls movement of solutes between internal fluids and external environment
Animal cells will swell and burst if continuous uptake of water, or shrivel and die is continuous net loss of water
Rates of water uptake and loss must balance...osmosis!

5. Osmoregulation-Osmosis
Osmosis: special case of diffusion in which water moves across a selectively permeable membrane when two solutions separated by the membrane differ in osmotic pressure, or osmolarity (measure of solute concentration: moles of solute per liter of solution)
Isoosmotic: two solutions have same osmolarity- no net movement of water (water molecules continuously crossing membrane but at equal rates)
Hypoosmotic: the more dilute solution when two solutions differ in osmolarity
Hyperosmotic: solution with greater concentration of solutes when two solutions differ in osmolarity

6. Osmoregulation Two ways to balance water gain with water loss:
Osoconformer (only marine animals): animal which does not actively adjust its internal osmolarity; isoosmotic to surroundings-internal osmolarity same to its environment so no tendency to gain or lose water
Live in water with stable composition so have a constant internal osmolarity
Osmoregulator: animal that must control its internal osmolarity because body fluids not isoosmotic with outside environment
Discharge excess water if in hypoosmotic environment
Take in water if in hyperosmotic environment
Can live in environments unsuitable for osoconformers (freshwater, terrestrial)

7. Osmoregulation Two type of organisms:
Stenohaline: can not tolerate substantial changes in external osmolarity
Euryhaline: can survive large fluctuations in external osmolarity (ex: salmon and tilapia)

8. Osmoregulation Adaptation in Marine Animals
Seawater dehydrates because much saltier than internal fluids
Lose water by osmosis and gain salts by diffusion
Drink large amounts of seawater to balance water loss
Kidneys remove salt from body
Small amounts of water in very concentrated urine

9. Osmoregulation Adaptation in Freshwater Animals
Osmolarity of internal fluids higher than surrounding environment
Gain water by osmosis and lose salts by diffusion
Adaptation to a lower salinity environment-lower solute concentrations in body fluids-reduced osmotic difference reduces energy needed for osmoregulation
Excrete large amounts of very dilute urine

10. Osmoregulation Adaptation in Animals that Live in Temporary Waters
Anhydrobiosis “life without water”: lose almost all their body water and survive in a dormant state when their habitats dry up
(a) Hydrated tardigrade
(b) Dehydrated
tardigrade
100 µm

11. Osmoregulation Adaptations in Land Animals
Threat of dessication
Lose water through surfaces in gas exchange organs, urine, feces, and skin
Adaptations to reduce water loss and maintain homeostasis
Body coverings
Waxy layers of insect exoskeletons
Layers of dead, keratinized skin cells of humans
fur
Nocturnal: lower temp, higher humidity of night
Drinking and eating moist foods
Using metabolic water (water produced during cellular respiration)

12. Osmoregulation
Ultimate function: maintain composition of cellular cytoplasm
Done by managing composition of internal body fluid that bathes cells
In a closed circulatory system, this is interstitial fluid (fluid composed of water, amino acids, sugars, fatty acids, coenzymes, hormones, neurotransmitters, and salts) controlled through the composition of blood
Specialized structures maintain fluid composition

13. Osmoregulation
Transport epithelium: layer or layers of specialized epithelial cells that regulate solute movements
Essential components of osmotic regulation and metabolic waste disposal
Move specific solutes in controlled amounts in specific direction
Directly face outside environment or line channels connected to outside by an opening on body surface
Impermeable tight junctions
Form barrier at tissue-environment boundary
Ensures solute moving between animal and environment passes through a selectively permeable membrane
Arranged in complex tubular networks with extensive surface areas
Ex: salt glands of marine birds

14. Nasal salt gland
Nostril
with salt
secretions
Lumen of
secretory tubule
NaCl
Blood
flow
Secretory cell
of transport
epithelium
Central
duct
Direction
of salt
movement
Transport
Secretory
tubule
Capillary
Vein
Artery
(a) An albatross’s salt glands empty via a duct into the nostrils, and the salty solution either drips off the tip of the beak or is exhaled in a fine mist.
(b) One of several thousand secretory tubules in a salt- excreting gland. Each tubule is lined by a transport epithelium surrounded by capillaries, and drains into a central duct.
(c) The secretory cells actively transport salt from the blood into the tubules. Blood flows counter to the flow of salt secretion. By maintaining a concentration gradient of salt in the tubule (aqua), this countercurrent system enhances salt transfer from the blood to the lumen of the tubule.